The Navier-Stokes equations, named after Claude-Louis Navier and George Gabriel Stokes, describe the motion of fluid substances. These equations arise from applying Newton's second law to fluid motion, together with the assumption that the fluid stress is the sum of a diffusing viscous term (proportional to the gradient of velocity), plus a pressure term.
The equations are useful because they describe the physics of many things of academic and economic interest. They may be used to model the weather, ocean currents, water flow in a pipe and air flow around a wing. The Navier-Stokes equations in their full and simplified forms help with the design of aircraft and cars, the study of blood flow, the design of power stations, the analysis of pollution, and many other things. Coupled with Maxwell's equations they can be used to model and study magneto-hydrodynamics.
Together with supplemental equations (for example, conservation of mass) and well formulated boundary conditions, the Navier-Stokes equations seem to model fluid motion accurately; even turbulent flows seem (on average) to agree with real world observations.
The Navier-Stokes equations assume that the fluid being studied is a continuum not moving at relativistic velocities. At very small scales or under extreme conditions, real fluids made out of discrete molecules will produce results different from the continuous fluids modelled by the Navier-Stokes equations. Depending on the Knudsen number of the problem, statistical mechanics or possibly even molecular dynamics may be a more appropriate approach.
Time tested formulations exist for common fluid families, but the application of the Navier-Stokes equations to less common families tends to result in very complicated formulations which are an area of current research. For this reason, these equations are usually written for Newtonian fluids. Studying such fluids is “simple” because the viscosity model ends up being linear; truly general models for the flow of other kinds of fluids, such as blood as of 2011, do not exist.
Solving the Navier-Stocks equations for an arbitrary fluid is an open problem in mathematics and of course, a very good modelling of such this fluid is strongly related to the membrane where the fluid flows on it. The blood as a complicated and Non-Newtonian fluid through the heart's chambers and heart's valves is one of the big challenges among mathematical-, medical-, physical- and computer-sciences. So far a lot of studies of the blood flowing through the heart have been attempted by various simple assumptions.
For instance, U.S. Pat. No. 5,537,641, assigned to University of Central Florida Research Foundation, Inc. discloses a method for generating a three-dimensional animation model that stimulates a fluid flow on a three-dimensional graphics display. The said patent does not extend the solution of Navier-Stokes equation to non-Newtonian fluids like blood explicitly.
U.S. Pat. No. 6,135,957 assigned to U.S. Philips Corporation describes a method of determining the viscosity and the pressure gradient in a blood vessel, including the acquisition of n≧2 blood speed values, corresponding to the same number of n radii of the blood vessel, determined along a diameter situated in a given axial position, formation of a blood speed vector by means of said n blood speed values, and evaluation of said viscosity and pressure gradient on the basis of a transformation of said blood speed value, including formation of a linear relation which directly links a flow rate vector (y) to the speed derivative vector (h), factorized by the viscosity (μ), and to the pressure gradient vector (σ), and simultaneous evaluation of the two values to be determined for the viscosity (μ) and the pressure gradient (σ) on the basis of said direct equation. The said method, as disclosed in U.S. '957, specifically used to determine blood speed, but seemingly does not disclose a method or system for modelling cardiac condition, specifically left ventricle having a main role in cardiac function based on flow.
Hence, the present inventors propose a novel system for solution of Navier-Stokes to model not only the normal blood flow inside the left ventricle but also for the other cavities and valves and model heart diseases.